Today, conventional twin-hull boats with hydrofoils are transversely equipped with a plurality of hydrofoils below the bottom of the stem and the stern extending across a twin hull.
In the course of securing a plurality of hydrofoils to the bottom of the stem and the stern of a twin-hull, predetermined hydrofoils are provisionally secured to the bottom of the completed twin hull and trial runs are executed by cruising the boat in this condition. Finally, based on the result of these trial runs, the optimal angle for securing hydrofoils to the twin-hull boat is eventually determined.
Nevertheless, in the case of the conventional twin-hull boat with hydrofoils cited above, since the optimal angle for securing hydrofoils to the twin-hull is determined in the final stage in order that the angle can be suited for cruising the boat at a very high speed, the determined angle cannot be optimal in the transitional period from the time in which hydrofoils remain still to the time at which the twin-hull boat starts to cruise with the hydrofoils afloat on the water surface.
Therefore, any conventional twin-hull boat with hydrofoils in service today necessarily spends much time in the transitional period before actually starting to cruise with the hydrofoils afloat on the water surface.
Even though there is a known twin-hull boat based on a system for swinging hydrofoils in order to vary the postural position of the hydrofoils, this in turn requires installation of a special device in limited space on the hull to permit swinging of the hydrofoils, and also involves much difficulty to install the device therein. In addition, total cost for manufacturing the twin-hull boat incorporating this system is quite high.